This invention can be used in various fields where constructions are tested for continuity defects in a contact fashion or combined with the remote method. Examples of device and method implementation may include pipes for oil and gas industry, detection of flaws in rolled products in metallurgical industry, welding quality of heavy duty equipment such as ships and reservoirs, etc. It is especially important for inspection of loaded constructions, such as pressured pipes, infrastructure maintenance, nuclear power plant monitoring, bridges, corrosion prevention and environment protection.
Similar to the modes of transportation like roads, railroads, and electric transmission lines, the pipelines have an important role in the nation's economy, belonging to the long linear assets. They typically cross large distances from the points of production and import facilities to the points of consumption. Like the other modes of transportation, pipe lines require very large initial investment to be built, having long exploitation periods when properly maintained. Like any engineering structure, pipelines do occasionally fail. While pipeline rates have little impact on the price of a fuel, its disruptions or lack of capacity can constrain supply, potentially causing very large price spikes. That's why pipelines, such as ones used in the oil and gas industry, require regular inspection and maintenance before potentially costly failures occur.
The major causes of pipeline failures around the world are external interference and corrosion; therefore, assessment methods are needed to determine the severity of such defects when they are detected in pipelines. Pipeline integrity management is the general term given to all efforts (design, construction, operation, maintenance, etc.) directed towards ensuring continuing pipeline integrity.
Traditional contact methods of assessing the structural integrity typically complemented by flaw detection using in-line inspection (ILI), detecting and evaluating various metal defects organized by area (clusters), assessing their danger by calculating a level of stress-deformed state (SDS), and deciding on a permissible operating pressure with evaluated factor of repair (EFR), based on residual pipe wall thickness (for defects of “metal loss”—corrosion type).
Pipelines, e.g. those used in the oil and gas industry, need regular inspection and maintenance before potentially costly failures occur. A traditional method of assessing the technical condition of a pipeline typically includes flaw detection using in-line inspection (ILI) for detecting location and evaluating parameters of separate metal defects, joining defects into clusters by an expert evaluation method (without indicating the rules of joining), calculating a level of stress deformed condition (SDC) in cluster zones to assess their danger, and calculating a permissible operating pressure and evaluated factor of repair (EFR) for clusters of corrosion origin based on residual pipe wall thickness with defects of “metal loss” (corrosion) type.
As a contact technique, pigging devices has been used for many years to maintain larger diameter pipelines in the oil industry. Today, however, the use of smaller diameter pigging devices is increasing in many plants as plant operators search for increased efficiencies and reduced costs. Unfortunately, the ILI using intelligent pigging is unavailable for a wide range objects that require full disruptive inspection and significant spending on repair preparation. While the ILI method is suitable for the initial flaw detection, it is less efficient for the relative degree (ranking) of the risk-factor evaluation, as well as for defective pipeline serviceability calculation.
Pipe-line pigging device can detect the following types of defects: i) changing in geometry: dents, wavy surface, deformed shape of cross-section; ii) metal loss, having mechanical, technological or corrosion nature; material discontinuity: layering and inclusions; iii) cracks; iv) all types of welding defects.
Pipe-line pigging is a very expensive and labor consuming method. The major limitation of this method is the fact that a large part of pipe-lines are not prepared for the pigging device operation, e.g. due to lack of input/output chambers for pig-flow device launching and pipe-line cleaning access, partially blocked pipe cross-section due to the welding artifacts, geometrical abnormalities and large slopes (small radius turns) of the pipe-line layout. In order to make the pipe-line pigging method possible, a significant preparation has to be done in advance, in particular, the high residual level magnetization (saturated magnetic fields) of the pipe line has to be performed before using the pig-flow device. This causes future technical problems of the pipeline demagnetization that required for actual pipe repair after the pigging.
Moreover, the evaluation of the absolute values of mechanical flaws by pigging device is particular difficult due to the multiple additional factors that have to be taken into account, e. g. bearing capacity of the soil, local cyclical loads (temperature, etc.).
Aside of the remote methods, there are numerous contact non-destructive testing devices for access to the surface of the metallic construction (ultrasound-, eddy-current-, magnetic-powder-defectoscopy). The main disadvantages of such methods is the time-consuming procedure of surface preparation that reduces the scope of applicability and leads to high cost, low registration sensitivity and selectivity for hidden internal defects identification.
Typically, a pipeline company will have a thorough pipeline safety program that will include a routine for the identification of pipeline defects and review of pipeline integrity. Such a plan should include, but not be limited to i) a review of previous inspection reports by a third party expert; ii) excavation of sites identified by this review for visual examination of anomalies; iii) repairs as necessary; and iv) addressing factors in the failure and verify the integrity of the pipeline.
It is important to mention that the pipeline safety program can be only as effective as the interpretation of internal inspection reports.
There are several magnetographic devices that have been disclosed for non-destructive inspection of ferrous materials. In magneto-graphic inspection and defectoscopy the tested area of the material is placed in proximity to the magnetic medium. The changes of the surface-penetrating impede flux due to the material flows or deviations can be recorded. The resulting “magnetogram” of the material can provide the information about the location, size, and type of the defect or abnormality. In general, this information can be converted into the report about the quality of the material. Obtaining the magnetogram (magnetic picture) of the material in the course of the non-destructive inspection process is very challenging and typically requires additional forms of inspection, such as roentgenogram or an X-ray image.
For example, U.S. Pat. No. 4,806,862 (Kozlov) offers a contact method of magnetographic inspection of quality of materials, where a magnetic substance (such as liquid) is applied to be magnetized together with the tested material. According to the invention, the intensity of the magnetizing field is established by the maximum curvature of the surface of a drop of a magnetic fluid applied onto the surface of the material to be inspected, so that the resulting magnetogram can be used to assess the quality of the material.
In another magnetographic U.S. Pat. No. 4,930,026 (Kljuev), the flaw sensor for magnetographic quality inspection is disclosed, which includes a flaw detector and a mechanism for driving the magneto-sensitive transducer. During the scanning procedure, the magnetic leakage fluxes penetrate through the surface of the material in places where flaws occur, resulting in a magnetogram of the tested material.
There is another magnetic technique that has been proposed by U.S. Pat. No. 6,205,859 (Kwun) to improve the defect detection with magnetostrictive sensors for piping inspection. The method involves exciting the magnetostrictive sensor transmitter by using a relatively broadband signal instead of a narrow band signal typically used in order to avoid signal dispersion effects. The amplified detected signal is transformed by a short-time Fourier transform providing the identifiable signal patterns from either defects or known geometric features in the pipe such as welds or junctions.
There is a known contact device with two single component collinear flux-gate magnetometers have been reported for the contact magnetometric monitoring and defects detection, RU 2062394. This device characterized by limited applicability due the slow data reception and processing and low sensitivity that makes impossible to detect minor deviations of stress-strain state (STS) from the background values, also leading to the low resolution threshold and a high false alarm rate.
The deviations of F-value can be classified as follows: X1—for negligible defects (good technical condition of the metal); X2—for defects that require planned repairs (acceptable technical condition); X3—for defects that require immediate repairs (unacceptable, pre-alarm technical condition, alarm).
The absolute values X1-X3 of the F-value (comprehensive value of magnetic field anomaly) should be defined for each particular case, depending upon the following factors: i) Material type (e.g. steel); ii) Topological location with the local background magnetic fields variation range, iii) Distance to the object (e.g. pipe-line installation depth), iv) General condition of the deformation-related tension within construction under testing, v) etc.
As a result, the only relative changes (variations) of the magnetic field can be evaluated for the given defective segment (relatively to the flawless segment), by comparing to its relative F-values. Thus, the very moment of the ultimate stress-limit crossing can be identified for each defective segment during the real operation (i.e. under pressure/loaded) condition. It can be done by monitoring the development of the defects within its F-value interval, namely, starting from the good technical condition X1 up until the yield-strength limit approaching and material breakdown. It provides a real possibility to predict the defect's speed development, resulting in increased accuracy in priority order definition for upcoming maintenance steps.
The aforementioned techniques are not satisfactory to be used for efficient prediction in defects development timeline and not capable of providing a real-time alert about the strength-limits approaching, i.e. when probable construction failure is about to occur.
The closest remote technology to the disclosed invention is shown in RU 2264617 that describes the Magnetic Tomography (MT) technique. This technique includes a remote magnetic field vectors measurement in Cartesian coordinates with the movement of measuring device (magnetometer) along the pipe-line, the recording of the anomalies of magnetic field (on top of background magnetic field), processing of the data and report on found pipe-line defects with their localization shown in resulting magnetogram. The technique provides a good sensitivity, also capable of discovering the following types of defects: i) Changing in geometry: dents, wavy surface, deformed shape of cross-section; ii) Metal loss, having mechanical, technological or corrosion nature; material discontinuity: layering and inclusions; iii) Cracks; iv) Welding, flaws, including girth weld defects. Moreover, such method provides a risk-factor ranking of the discovered pipe-line defects accordingly to material tension concentration (factor F). Accordingly this technique was taken as initial prototype for the disclosed technology.
MT determines the comparative degree of danger of defects by a direct quantitative assessment, of the stress deformed condition of the metal. Conventional surveys only measure the geometrical parameters of a defect. Their subsequent calculations to assess the impact of the defect on the safe operation of the pipe do not take into consideration the stress caused by the defect. Therefore conventional surveys may fail to detect dangerously stressed areas of the pipe or, conversely, classify a defect as one which requires urgent attention when, in reality, the stress level may be low and the defect presents no immediate threat to the operation of the pipe. Since MT directly measures the stress caused by defects it is an inherently more accurate guide to the safe operation of the pipeline than conventional survey methods.
There are several methods for integrity assessment of extended structures (e.g. metallic pipes) that have been proposed in literature. Thus, U.S. Pat. No. 4,998,208 (Buhrow, et al) discloses the piping corrosion monitoring system that calculates the risk-level safety factor producing an inspection schedule. There is another method disclosed in U.S. Pat. No. 6,813,949 (Masaniello, et al.), which addresses a pipeline inspection system having a serviceability acceptance criteria for pipeline anomalies, specifically wrinkles, with an improved method of correlating ultrasonic test data to actual anomaly characteristics.
The main disadvantages of previous methods are: i) The scope of its application is limited by large-scale linear objects. Located at a considerable distance from each other, ii) Difficult real-time implementation of the device, iii) It is impossible to identify the location of individual defects, visualize and specify the exact position on the internal or external tested surfaces; iv) There is also a lack of visualization of the obtained information in a form of the resulting tomogram where all the locations of the defective segments with associated respective risk factors (absolute mechanical stress values) are shown.
There is a need in developing a combination of contact and remote techniques in order to increase sensitivity, resolution and visual representation of the stress-related anomalies within the structure, as well as a probability of operation failure (i.e. risk-factor).
The defect areas risk-factor criteria and ranking (such as material stress: F-value) is used for planning a required sequence of repair and maintenance steps. Such criteria were developed by comparing a risk-factor calculated using the defect geometry in calibration bore pits with a predicted risk-factor obtained by the remote magneto-metric data (i.e. comprehensive F-value of particular magneticanomaly).
However, there are several limitations to the above method. For example, ILI using intelligent pigging is unavailable for a range of objects that are non-piggable, or requires significant spending to prepare an object for pigs running. While the ILI method is suitable for the first task (the flaw detection itself), it is less advantageous for evaluating the comparative degree of the flaw's danger (e.g. by ranking), or for calculating serviceability of pipeline sections with various defects. Also, traditional calculations consist only in the evaluation of danger of groups of defects (clusters) like “metal loss”. The task of evaluating the corrosion rate (corrosion prognosis or monitoring) is not solved, and is typically settled by repeated runs of tools-defectoscopes.
Furthermore, in the above traditional method, there is no evaluation of cracks stability, that is, no prognosis for the rate of crack-like defects development, especially in a longitudinal direction. There is also no evaluation of danger of other types of defects (e.g. welds) due to operation conditions, as the evaluation of metal properties degradation in aggressive conditions and with anomalies of stress-deformed condition (SDC) is not carried out. For example, there are pipeline sections with sags, bends, stresses/stretches/twists, that is, with loss of a pipeline stability, e.g. due to land-washing during heavy rains, in land-slipping areas, precipices, ravines and zones of seismic activity. In addition, the main problem—the degree of stress concentration in a particular pipeline section—is not considered; it must be considered by engineers of the integrity department of the company/operator by e.g. expert evaluation.
As an alternative to the above method, a magnetometric tomography method (MTM) has been proposed. MTM is a non-contact method of non-destructive testing (NDT) and technical diagnostics based on remote scanning the magnetic field of a ferro-magnetic pipeline in a system of orthogonal coordinates. Additionally, manual processing and calibrating are used to define locations of sections with metal defects of various types, identify the type of the most dangerous defects, and evaluate serviceability of defective sections according to the degree of mechanical stress concentration.
However, MTM is currently available only to on-shore (i.e. land-based) applications. Also, the current detection capability of such a magnetometer is only up to a maximum distance of 20 times the pipe diameter. Thus, such conventional MTM systems are not suitable for many subsea (i.e. underwater) pipelines, which may be located at significant depths. The inspection speed is also limited to only about 2 meters per second (m/s), and the recording of distance is typically manual. Also, the analysis of the collected data is substantially manual, i.e. it relies again on expert evaluation.
A need therefore exists to provide a system and method for inspecting a subsea pipeline that seeks to address at least some of the above problems.